1. Field of the Invention
The present invention relates to an optical recording and/or reproducing apparatus, such as a photodisk and the like, which carries out operation of recording and/or reproducting information using light, and more in particular to an optical recording and/or reproducing apparatus wherein the surface of the data carrier is vertical to the optical axis of beam irradiated on the surface.
2. Description of the Prior Art
FIG. 1 is a sectional view showing a conventional optical recording and/or reproducing apparatus as disclosed in the Japanese Patent Laid-open No. 57-186237 (1982). In the Figure, the numeral 1 denotes a disk-shaped data carrier capable of carrying out operations of recording and/or reproducing information using light. The data carrier 1 is supported by a turntable 3. Rotation of a spindle motor 2 is transmitted to the turntable 3 so that the data carrier 1 can turn around its central axis. The data carrier 1 is pressed to the turntable 3 with a clamp 4 which holds the data carrier 1 and turns together with the data carrier 1, while the clamp 4 is subjected to pressure and supported to be capable of turning around by a support member 5.
Under the data carrier 1, there is provided a slide base 6 which is capable of driving in the radial direction of the data carrier 1, while above the slide base 6 there is provided an optical head 7 for radiating a beam to the data carrier 1. The optical head 7 is held by a support axis 8 to be capable of oscillating above the slide base 6. An objective lens 9 is mounted at an opening for emitting the beam from the optical head 7 being movable in the direction of an optical axis 10 of the beam (in the focus direction) and in the vertical direction to the optical axis 10 (in the tracking direction). Furthermore, a tilt-servomechanism 11 is provided on the slide base 6 so that the optical head 7 can oscillate around the support axis 8.
FIG. 2 is an enlarged sectional view showing a diver-gence-detecting means 12 for detecting divergences from right angles between the optical axis 10 and the surface of the data carrier 1. In the figure, the detecting means 12 comprises a radiating element 13, light-receiving elements 14, 15 disposed at an equal distance from the radiating element 13 with the radiating element 13 therebetween and a calculation amplifier 16 which amplifies the signal being output from the light-receiving elements 14, 15 and calculates it. Thus the detecting means 12 detects the extent of tilt of the surface of the data carrier 1 to the detecting means 12 by the difference in the amount of the light received by the two light-receiving elements 14, 15 which receive the reflected light from the data carrier 1 to turn the extent of tilt of the surface to the optical axis 10 into the output signal from the calculation amplifier 16.
In an optical recording and/or reproducing apparatus of such a construction as described above, the data carrier 1 is disposed between the turntable 3 and the clamp 4 and driven to turn by the spindle motor 2, as shown in FIG. 1. In such a case, the data carrier 1 is deformed, generally into an armlike shape as shown in the drawing, because of a shrinkage caused immediately after molding, a secular change, a change in temperature and the like.
When the slide base 6 is driven in the radial direction of the data carrier 1 to reach under the surface of the tilted region near the outer peripheral portion of the data carrier 1, it comes to be impossible that the optical axis 10 of the beam, which is radiated from the optical head 7 above the slide base 6, and the surface of the data carrier 1 should be vertical. The divergence-detecting means 12 as shown in FIG. 2 detects this state and the tilt-servomechanism 11 operates in response to the signal from the calculation amplifier 16 to make the optical head 7 turn around the support axis 8, so that the optical axis 10 can be vertical to the surface of the data carrier 1.
In the case where the divergence from right angles between the optical axis 10 and the surface of the data carrier 1 is kept, a distortion occurs in the shape of the condensing spot converged on the surface, pits (perforations) corresponding to information can not exactly be formed on the surface in recording information, while such problems as a decrease of the C/N ratio and an increase of an error in reproducing information should occur. In addition, troubles will happen in controlling, or in maintaining the condensing spot on the surface (the tracks). In a digital photodisk of a tracking control method wherein the condensing spot is made to follow the surface (the tracks) using a diffracted light method or the like, recording errors of the information signals increase.
Since aforementioned troubles will occur in the case where a divergence from right angles made by the optical axis 10 and the surface of the data carrier 1, the right angles should be kept by making the optical head 7 oscillate by means of the tilt-servomechanism 11. In such a case since the objective lens 9 also shifts, the distance between the objective lens 9 and the surface of the data carrier 1 greatly changes. That is, as shown in FIG. 1, the above-said distance greatly varies from A at a point where the surface of the data carrier 1 remains horizontal to B at a point where that of the data carrier 1 is titling. In order to overcome such a difference in distance, the objective lens 9 is made to conduct parallel translations in the direction of the optical axis 10 to converge the beam on the surface of the data carrier 1.
The data carrier 1 is housed in a housing as disclosed, for example, in Japanese Patent Application Laid-open No. 61-287088 (1986). The housing 19 is shown in FIG. 3, wherein an opening 21 for inserting the head is provided in such a manner that it is capable of opening and closing by a shutter 20 mounted slidably in the direction of an arrow (a) in the figure.
In a conventional optical recording and/or reproducing apparatus as shown above, it has been necessary to shift the objective lens 9 on the optical head 7 substantially in the direction of the optical axis 10 for the purpose of focalizing, which has resulted in that a large-sized optical head 7 has been required. Moreover, as for the tilt-servomechanism 11 for oscillating the optical head 7, a large-sized one had been required. As a result, their great amount of weight on the slide base 6 which drives in the radial direction of the data carrier 1 has made high-speed driving (highspeed accessibility to informations) to be difficult.